The explorer package utilizes frontier based exploration to discover environments autonomously operating a distributed multi-robot system. Beside frontier detection, coordinated and uncoordinated exploration strategies are available to select goal points. Coordinated exploration enhances robot distribution and reduces redundancy in exploration which result in improvement of efficiency in terms of exploration time.

Overview

The explorer package comprises multiple functionalities to perform frontier based exploration. Frontier detection is utilized on local and global costmaps to further select navigation goals in the environment to proceed with exploration. The assignment of robots to goals is accomplished according to coordinated and uncoordinated exploration strategies being applied for the distributed multi-robot system.

Auctioning thereby ensures negotiation among available goals to coordinate efficiently, distributing robots among the environment by minimizing the overall travel path. Additionally to frontier detection and selection, the explorer package is concerned with navigation to goal points by incorporating a simple action client utilizing move_base.

Exploration

Frontier based exploration is available for single and multi-robot systems. The exploration package is capable to operate in Simulation, e.g. Stage, but also to be deployed on a real robot system, e.g. Turtlebots and Pioneers. Additionally, coordinated robots comprise multiple frontiers as clusters to spatially interrelate groups of frontiers. Hence, multi-robot distribution is improved and number of participating goals, e.g. clusters, is narrowed. As a consequence, robots auction among clusters, implying less effort to negotiate a narrowed subset of elements.

Single Robot Exploration

As a single robot explores, communicational capabilities are irrelevant and exploration strategy is uncoordinated. Frontiers are therefore detected and selected according to "Nearest Frontier" strategy. The following video depicts single robot exploration utilizing Stage and "Nearest Frontier" strategy. Robots detect frontiers and represent them accordingly as red spheres in RVIZ, indicating selected frontiers as pink sphere.

Multi Robot Exploration

As a multi-robot exploration is assumed, robots maintaining a communication link to each other are capable to coordinate on cluster level. Thus, efficiency of exploration is increased as multiple robots distribute among the environment to explore different areas. Such a coordinated approach is depicted in the following video, utilizing two robots to decrease exploration time. Further, available clusters are represented by underlying frontiers with different colors. In the video, two robots explore an environment emulated by Stage, where one robot is depicted in RVIZ visualizing clusters, frontiers and selected goal points.

Related Documentation

Please refer to the following paper to retrieve more information on the node:

ROS API

Exploration Package

The explorer package publishes multiple topics to depict frontiers, clusters and goal points in RVIZ and to coordinate among multiple other robots participating in exploration. Further, required topics to be subscribed are listed.